1. Field of the Invention
The present invention relates to a heat sink for enlarging a heat exchanging area in various heat exchanging devices or heat transfer devices and, more particularly, to a process for manufacturing a heat sink, which is constructed to protrude a number of radiation members into a base portion, and an apparatus for carrying out the process.
2. Related Art
In order to improve the heat exchanging capacity of a thermal device such as a heat pipe by enlarging the heat radiating or absorbing area, it is widely executed in the prior art to employ a heat sink.
An example of this kind of heat sink is shown in FIGS. 30A and 30B. A heat sink 1, as shown in FIG. 30A, is equipped with a plurality of plate-shaped fins 2 arrayed in parallel with one another, and a plate-shaped base 3 projecting the fins 2. The heat sink 1 thus constructed is generally manufactured in the prior art by the extruding method using an aluminum alloy. In the heat sink 1 shown in FIG. 30B, on the other hand, the fins 2 acting as the radiation members are formed into a circular column shape. Moreover, the heat sink shown in FIG. 30B is generally manufactured in the prior art by the forging method using a copper alloy.
The fins 2 of the heat sink 1 are preferably arrayed as dense as possible. On the other hand, however, the extruding or forging method, as adopted as the method for manufacturing each of the aforementioned heat sinks 1, is intended to form the target shape by fluidizing the material. It is, therefore, necessary to introduce the material into the small clearances corresponding to the fins in the forming mold, when the heat sink is to be manufactured by the extruding or forging method. For the smaller sectional area of the clearances and for the longer introduction (corresponding to the length of the fins 2), however, the material becomes the more reluctant to flow. In the prior art, therefore, the minimum thickness t of the fins 2 is limited by about 2 mm. When the thickness t is set to 2 mm, the maximum height (or length) h of the fins 2 is limited by about 20 mm. From the requirement of the strength of the mold, on the other hand, the array pitch p of the fins 2 has to be 5 mm or more.
When the heat sink 1 is to be thus manufactured by the extruding or forging method, the fins 2 cannot be made thin and high, and the number of the fins 2 per unit area of the base 3 is restricted. This raises a disadvantage that the heat exchanging area of the heat sink to be achieved by the conventional method is restricted to a small value.
An invention capable of eliminating such a disadvantage is disclosed in Japanese Patent Laid-Open No. 9-181231. The conventional process, as disclosed in this Laid-Open, will be briefly described with reference to FIGS. 31 and 32. In a heat sink 4 manufactured by this process, rectangular and thin fins 6 are integrated with a plate-shaped base 5. The fins 6 are prepared by cutting a rolled sheet of an aluminum alloy into a rectangular shape. These fins 6 are arrayed at a constant pitch by inserting them liquid-tight into the (not-shown) slits formed in the mold. Moreover, the one-end portions of the individual fins 6 are protruded from the mold. In this state, a molten metal of the aluminum alloy is poured into the end portions, as protruded from the mold of the fins 6 to form the shape of the base 5. Immediately before the complete solidification, moreover, the molten metal is pressurized for the forging effect.
According to this process, what is used is the fins 6 prepared prior to casting but not the casting fins 6, so that the thickness, height or pitch of the fins 6 is not restricted. Since the molten metal is pressurized midway of solidification, moreover, the defects such as air bubbles and so on in the base 5 can be eliminated.
According to the aforementioned conventional method of forming the base by casting forging the molten metal, however, the mold is closed after it is fed with the molten metal for the base, and the molten metal is pressurized to raise a problem that the time period required for molding the base is elongate to deteriorate the productivity. Moreover, the fins are made of the thin sheets, as described above, or replaced by thin pins. The fins of this structure are low in their own strength and are heated and cooled at the time of molding the base. This raises another disadvantage that the strength is further lowered. The fins thus having lowered the strength are deformed while they are being used. As a result, the adjoining fins come into contact to invite a problem that their radiation area is reduced to deteriorate the radiation efficiency.